Remove dead macro exec_subplan_get_plan

When Who What
2023-04-04 18:03:56 Greg Stark (stark) Closed in commitfest 2023-03 with status: Rejected
2023-01-31 16:18:25 vigneshwaran C (vignesh.postgres) Closed in commitfest 2023-01 with status: Moved to next CF
2022-12-11 06:32:32 Ian Barwick (barwick) Closed in commitfest 2022-11 with status: Moved to next CF
2022-11-12 20:12:25 Tom Lane (tgl) Removed tgl from reviewers
2022-11-05 15:03:15 Tom Lane (tgl) New status: Needs review
2022-09-16 07:22:46 Mingli Zhang (zml) New status: Ready for Committer
2022-09-16 07:22:14 Mingli Zhang (zml) Changed reviewers to Tom Lane (tgl), Richard Guo (richardguo)
2022-09-16 07:20:47 Mingli Zhang (zml) Changed authors to Mingli Zhang (zml)
2022-09-16 07:18:52 Mingli Zhang (zml) Changed targetversion to 16
2022-09-16 07:17:51 Mingli Zhang (zml) Attached mail thread 85a0be98-a6d3-4760-952b-9cebdc51adfb@Spark
2022-09-16 07:17:51 Mingli Zhang (zml) Created patch record